Before making a backup, you must identify all the files in your database and decide what to back up. Several V$ views can provide the necessary information.

Listing Database Files Before a Backup

Use V$DATAFILE, V$LOGFILE and V$CONTROLFILE to identify the datafiles, log files and control files for your database. This same procedure works whether you named these files manually or allowed Oracle Managed Files to name them.

To list datafiles, online redo logs, and control files:

Start SQL*Plus and query V$DATAFILE to obtain a list of datafiles. For example, enter:

SQL> SELECT NAME FROM V$DATAFILE;

You can also join the V$TABLESPACE and V$DATAFILE views to obtain a listing of datafiles along with their associated tablespaces:

Obtain the filenames of online redo log files by querying the V$LOGFILE view. For example, issue the following query:

SQL> SELECT MEMBER FROM V$LOGFILE;

Obtain the filenames of the current control files by querying the V$CONTROLFILE view. For example, issue the following query:

SQL> SELECT NAME FROM V$CONTROLFILE;

Note that you only need to back up one copy of a multiplexed control file.

If you plan to take a control file backup with the ALTERDATABASEBACKUPCONTROLFILETO'filename' statement, then save a list of all datafiles and online redo log files with the control file backup. Because the current database structure may not match the database structure at the time a given control file backup was created, saving a list of files recorded in the backup control file can aid the recovery procedure.

Determining Datafile Status for Online Tablespace Backups

To check whether a datafile is part of a current online tablespace backup, query the V$BACKUP view.

This view is useful only for user-managed online tablespace backups, because neither RMAN backups nor offline tablespace backups require the datafiles of a tablespace to be in backup mode.

The V$BACKUP view is most useful when the database is open. It is also useful immediately after an instance failure because it shows the backup status of the files at the time of the failure. Use this information to determine whether you have left any tablespaces in backup mode.

V$BACKUP is not useful if the control file currently in use is a restored backup or a new control file created after the media failure occurred. A restored or re-created control file does not contain the information the database needs to populate V$BACKUP accurately. Also, if you have restored a backup of a file, this file's STATUS in V$BACKUP reflects the backup status of the older version of the file, not the most current version. Thus, this view can contain misleading data about restored files.

For example, the following query displays which datafiles are currently included in a tablespace that has been placed in backup mode:

In the STATUS column, NOTACTIVE indicates that the file is not currently in backup mode (that is, you have not executed the ALTERTABLESPACE...BEGINBACKUP or ALTER DATABASE BEGIN BACKUP statement), whereas ACTIVE indicates that the file is currently in backup mode.

You can make a whole database backup of all files in a database after the database has been shut down with the NORMAL, IMMEDIATE, or TRANSACTIONAL options. A whole database backup taken while the database is open or after an instance failure or SHUTDOWNABORT is inconsistent. In such cases, the files are inconsistent with respect to the checkpoint SCN.

You can make a whole database backup if a database is operating in either ARCHIVELOG or NOARCHIVELOG mode. If you run the database in NOARCHIVELOG mode, however, the backup must be consistent; that is, you must shut down the database cleanly before the backup.

The set of backup files that results from a consistent whole database backup is consistent because all files are checkpointed to the same SCN. You can restore the consistent database backup without further recovery. After restoring the backup files, you can perform additional recovery steps to recover the database to a more current time if the database is operated in ARCHIVELOG mode. Also, you can take inconsistent whole database backups if your database is in ARCHIVELOG mode.

Control files play a crucial role in database restore and recovery. For databases running in ARCHIVELOG mode, Oracle Corporation recommends that you back up control files with the ALTERDATABASEBACKUPCONTROLFILETO'filename' statement.

Making Consistent Whole Database Backups

This section describes how to back up the database with an operating system utility.

To make a consistent whole database backup:

If the database is open, use SQL*Plus to shut down the database with the NORMAL, IMMEDIATE, or TRANSACTIONAL options.

Use an operating system utility to make backups of all datafiles as well as all control files specified by the CONTROL_FILES parameter of the initialization parameter file. Also, back up the initialization parameter file and other Oracle product initialization files. To find these files, do a search for *.ora starting in your Oracle home directory and recursively search all of its subdirectories.

For example, you can back up the datafiles, control files and archived logs to /disk2/backup as follows:

You can back up all or some of the datafiles of an individual tablespace while the tablespace is offline. All other tablespaces of the database can remain open and available for systemwide use. You must have the DBA privilege or have the MANAGETABLESPACE system privilege to take tablespaces offline and online.

Note the following guidelines when backing up offline tablespaces:

You cannot offline the SYSTEM tablespace or a tablespace with active rollback segments. The following procedure cannot be used for such tablespaces.

Assume that a table is in tablespace Primary and its index is in tablespace Index. Taking tablespace Index offline while leaving tablespace Primary online can cause errors when DML is issued against the indexed tables located in Primary. The problem only manifests when the access method chosen by the optimizer needs to access the indexes in the Index tablespace.

To back up offline tablespaces:

Before beginning a backup of a tablespace, identify the tablespace's datafiles by querying the DBA_DATA_FILES view. For example, assume that you want to back up the users tablespace. Enter the following in SQL*Plus:

You can back up all or only specific datafiles of an online tablespace while the database is open. The procedure differs depending on whether the online tablespace is read/write or read-only.

Note:

You should not back up temporary tablespaces.

Making User-Managed Backups of Online Read/Write Tablespaces

You must put a read/write tablespace in backup mode to make user-managed datafile backups when the tablespace is online and the database is open. The ALTERTABLESPACE ... BEGINBACKUP statement places a tablespace in backup mode. In backup mode, the database copies whole changed data blocks into the redo stream. After you take the tablespace out of backup mode with the ALTERTABLESPACE...ENDBACKUP or ALTERDATABASEENDBACKUP statement, the database advances the datafile header to the current database checkpoint.

When restoring a datafile backed up in this way, the database asks for the appropriate set of redo log files to apply if recovery be needed. The redo logs contain all changes required to recover the datafiles and make them consistent.

To back up online read/write tablespaces in an open database:

Before beginning a backup of a tablespace, identify all of the datafiles in the tablespace with the DBA_DATA_FILES data dictionary view. For example, assume that you want to back up the users tablespace. Enter the following:

Mark the beginning of the online tablespace backup. For example, the following statement marks the start of an online backup for the tablespace users:

SQL> ALTER TABLESPACE users BEGIN BACKUP;

Caution:

If you do not use BEGINBACKUP to mark the beginning of an online tablespace backup and wait for that statement to complete before starting your copies of online tablespaces, or then the datafile copies produced are not usable for subsequent recovery operations. Attempting to recover such a backup is risky and can return errors that result in inconsistent data. For example, the attempted recovery operation can issue a "fuzzy files" warning, and can lead to an inconsistent database that you cannot open.

Back up the online datafiles of the online tablespace with operating system commands. For example, UNIX users might enter:

After backing up the datafiles of the online tablespace, run the SQL statement ALTERTABLESPACE with the ENDBACKUP option. For example, the following statement ends the online backup of the tablespace users:

SQL> ALTER TABLESPACE users END BACKUP;

Archive the unarchived redo logs so that the redo required to recover the tablespace backup is archived. For example, enter:

SQL> ALTER SYSTEM ARCHIVE LOG CURRENT;

Caution:

If you fail to take the tablespace out of backup mode, then Oracle continues to write copies of data blocks in this tablespace to the online logs, causing performance problems. Also, you will receive an ORA-01149 error if you try to shut down the database with the tablespaces still in backup mode.

Making Multiple User-Managed Backups of Online Read/Write Tablespaces

When backing up several online tablespaces, you can back them up either serially or in parallel. Use either of the following procedures depending on your needs.

Backing Up Online Tablespaces in Parallel

You can simultaneously create datafile copies of multiple tablespaces requiring backups in backup mode. Note, however, that by putting all tablespaces in online mode at once, you can generate large redo logs if there is heavy update activitiy on the affected tablespaces, because the redo must contain a copy of each changed data block in each changed datafile. Be sure to consider the size of the likely redo before using the procedure outlined here.

To back up online tablespaces in parallel:

Prepare all online tablespaces for backup by issuing all necessary ALTERTABLESPACE statements at once. For example, put tablespaces users, tools, and indx in backup mode as follows:

Again, it you are handling all datafiles at once you can use the ALTER DATABASE command instead of ALTER TABLESPACE:

SQL> ALTER DATABASE END BACKUP;

Archive the online redo logs so that the redo required to recover the tablespace backups will be available for later media recovery. For example, enter:

SQL> ALTER SYSTEM ARCHIVE LOG CURRENT;

Backing Up Online Tablespaces Serially

You can place all tablespaces requiring online backups in backup mode one at a time. Oracle Corporation recommends the serial backup option because it minimizes the time between ALTERTABLESPACE...BEGIN/ENDBACKUP statements. During online backups, more redo information is generated for the tablespace because whole data blocks are copied into the redo log.

To back up online tablespaces serially:

Prepare a tablespace for online backup. For example, to put tablespace users in backup mode enter the following:

SQL> ALTER TABLESPACE users BEGIN BACKUP;

In this case you probably do not want to use ALTER DATABASE BEGIN BACKUP to put all tablespaces in backup mode simultaneously, because of the unnecessary volume of redo log information generated for tablespaces in online mode.

Archive the unarchived redo logs so that the redo required to recover the tablespace backups is archived. For example, enter:

SQL> ALTER SYSTEM ARCHIVE LOG CURRENT;

Ending a Backup After an Instance Failure or SHUTDOWN ABORT

The following situations can cause a tablespace backup to fail and be incomplete:

The backup completed, but you did not run the ALTERTABLESPACE...ENDBACKUP statement.

An instance failure or SHUTDOWNABORT interrupted the backup.

Whenever crash recovery is required, if a datafile is in backup mode when an attempt is made to open it, then the database will not open the database until either a recovery command is issued, or the datafile is taken out of backup mode.

For example, the database may display a message such as the following at startup:

If the database indicates that the datafiles for multiple tablespaces require media recovery because you forgot to end the online backups for these tablespaces, then so long as the database is mounted, running the ALTERDATABASEENDBACKUP statement takes all the datafiles out of backup mode simultaneously.

In high availability situations, and in situations when no DBA is monitoring the database, the requirement for user intervention is intolerable. Hence, you can write a crash recovery script that does the following:

Mounts the database

Runs the ALTERDATABASEENDBACKUP statement

Runs ALTERDATABASEOPEN, allowing the system to come up automatically

An automated crash recovery script containing ALTERDATABASEENDBACKUP is especially useful in the following situations:

Mount the database, then run ALTERTABLESPACE...ENDBACKUP for each tablespace still in backup mode.

Ending Backup Mode with the ALTER DATABASE END BACKUP Statement

You can run the ALTERDATABASEENDBACKUP statement when you have multiple tablespaces still in backup mode. The primary purpose of this command is to allow a crash recovery script to restart a failed system without DBA intervention. You can also perform the following procedure manually.

To take tablespaces out of backup mode simultaneously:

Mount but do not open the database. For example, enter:

SQL> STARTUP MOUNT

If performing this procedure manually (that is, not as part of a crash recovery script), query the V$BACKUP view to list the datafiles of the tablespaces that were being backed up before the database was restarted:

Issue the ALTERDATABASEENDBACKUP statement to take all datafiles currently in backup mode out of backup mode. For example, enter:

SQL> ALTER DATABASE END BACKUP;

You can use this statement only when the database is mounted but not open. If the database is open, use ALTERTABLESPACE...ENDBACKUP or ALTERDATABASEDATAFILE...ENDBACKUP for each affected tablespace or datafile.

Caution:

Do not use ALTERDATABASEENDBACKUP if you have restored any of the affected files from a backup.

Ending Backup Mode with the SQL*Plus RECOVER Command

The ALTERDATABASEENDBACKUP statement is not the only way to respond to a failed online backup: you can also run the SQL*Plus RECOVER command. This method is useful when you are not sure whether someone has restored a backup, because if someone has indeed restored a backup, then the RECOVER command brings the backup up to date. Only run the ALTERDATABASEENDBACKUP or ALTERTABLESPACE...ENDBACKUP statement if you are sure that the files are current.

Note:

The RECOVER command method is slow because the database must scan redo generated from the beginning of the online backup.

Making User-Managed Backups of Read-Only Tablespaces

When backing up an online read-only tablespace, you can simply back up the online datafiles. You do not have to place the tablespace in backup mode because the system is permitting changes to the datafiles.

If the set of read-only tablespaces is self-contained, then in addition to backing up the tablespaces with operating system commands, you can also export the tablespace metadata with the transportable tablespace functionality. In the event of a media error or a user error (such as accidentally dropping a table in the read-only tablespace), you can transport the tablespace back into the database.

Before beginning a backup of a read-only tablespace, identify all of the tablespace's datafiles by querying the DBA_DATA_FILES data dictionary view. For example, assume that you want to back up the history tablespace:

Back up the online datafiles of the read-only tablespace with operating system commands. You do not have to take the tablespace offline or put the tablespace in backup mode because users are automatically prevented from making changes to the read-only tablespace. For example:

% cp $ORACLE_HOME/oradata/trgt/history*.dbf /disk2/backup/

Note:

When restoring a backup of a read-only tablespace, take the tablespace offline, restore the datafiles, then bring the tablespace online. A backup of a read-only tablespace is still usable if the read-only tablespace is made read/write after the backup, but the restored backup will require recovery.

Optionally, export the metadata in the read-only tablespace. By using the transportable tablespace feature, you can quickly restore the datafiles and import the metadata in case of media failure or user error. For example, export the metadata for tablespace history as follows:

Back up the control file of a database after making a structural modification to a database operating in ARCHIVELOG mode. To back up a database's control file, you must have the ALTERDATABASE system privilege.

Backing Up the Control File to a Binary File

The primary method for backing up the control file is to use a SQL statement to generate a binary file. A binary backup is preferable to a trace file backup because it contains additional information such as the archived log history, offline range for read-only and offline tablespaces, and backup sets and copies (if you use RMAN). Note that binary control file backups do not include tempfile entries.

To back up the control file after a structural change:

Make the desired change to the database. For example, you may create a new tablespace:

CREATE TABLESPACE tbs_1 DATAFILE 'file_1.f' SIZE 10M;

Back up the database's control file, specifying a filename for the output binary file. The following example backs up a control file to /disk1/backup/cf.bak:

ALTER DATABASE BACKUP CONTROLFILE TO '/disk1/backup/cf.bak' REUSE;

Specify the REUSE option to make the new control file overwrite one that currently exists.

Backing Up the Control File to a Trace File

The TRACE option of the ALTERDATABASEBACKUPCONTROLFILE statement helps you manage and recover the control file. The TRACE option prompts the database to write SQL statements to the database's trace file rather than generate a binary backup. The statements in the trace file start the database, re-create the control file, and recover and open the database appropriately.

To back up the control file to a trace file, mount or open the database and issue the following SQL statement:

ALTER DATABASE BACKUP CONTROLFILE TO TRACE;

If you specify neither the RESETLOGS nor NORESETLOGS option in the SQL statement, then the resulting trace file contains versions of the control file for both RESETLOGS and NORESETLOGS options. Tempfile entries are included in the output using "ALTER TABLESPACE... ADD TEMPFILE" statements.

You issue the following statement to create a trace file containing a CREATECONTROLFILE...NORESETLOGS statement:

ALTER DATABASE BACKUP CONTROLFILE TO TRACE NORESETLOGS;

You then edit the trace file to create a script that creates a new control file for the sales database based on the control file that was current when you generated the trace file. To avoid recovering offline normal or read-only tablespaces, edit them out of the CREATECONTROLFILE statement in the trace file. When you open the database with the re-created control file, the dictionary check code will mark these omitted files as MISSING. You can run an ALTERDATABASERENAMEFILE statement renames them back to their original filenames.

For example, you can edit the CREATECONTROLFILE...NORESETLOGS script in the trace file as follows, renaming files labeled MISSING:

# The following statements will create a new control file and use it to open the
# database. Log history and RMAN metadata will be lost. Additional logs may be
# required for media recovery of offline datafiles. Use this only if the current
# version of all online logs are available.
STARTUP NOMOUNT
CREATE CONTROLFILE REUSE DATABASE SALES NORESETLOGS ARCHIVELOG
MAXLOGFILES 32
MAXLOGMEMBERS 2
MAXDATAFILES 32
MAXINSTANCES 16
MAXLOGHISTORY 1600
LOGFILE
GROUP 1
'/diska/prod/sales/db/log1t1.dbf',
'/diskb/prod/sales/db/log1t2.dbf'
) SIZE 100K
GROUP 2
'/diska/prod/sales/db/log2t1.dbf',
'/diskb/prod/sales/db/log2t2.dbf'
) SIZE 100K,
GROUP 3
'/diska/prod/sales/db/log3t1.dbf',
'/diskb/prod/sales/db/log3t2.dbf'
) SIZE 100K
DATAFILE
'/diska/prod/sales/db/database1.dbf',
'/diskb/prod/sales/db/filea.dbf'
;
# This datafile is offline, but its tablespace is online. Take the datafile
# offline manually.
ALTER DATABASE DATAFILE '/diska/prod/sales/db/filea.dbf' OFFLINE;
# Recovery is required if any datafiles are restored backups,
# or if the most recent shutdown was not normal or immediate.
RECOVER DATABASE;
# All redo logs need archiving and a log switch is needed.
ALTER SYSTEM ARCHIVE LOG ALL;
# The database can now be opened normally.
ALTER DATABASE OPEN;
# The backup control file does not list read-only and normal offline tablespaces
# so that Oracle can avoid performing recovery on them. Oracle checks the data
# dictionary and finds information on these absent files and marks them
# 'MISSINGxxxx'. It then renames the missing files to acknowledge them without
# having to recover them.
ALTER DATABASE RENAME FILE 'MISSING0002'
TO '/diska/prod/sales/db/fileb.dbf';

To save disk space in your primary archiving location, you may want to back up archived logs to tape or to an alternative disk location. If you archive to multiple locations, then only back up one copy of each log sequence number.

To back up archived redo logs:

To determine which archived redo log files that the database has generated, query V$ARCHIVED_LOG. For example, run the following query:

SELECT THREAD#,SEQUENCE#,NAME
FROM V$ARCHIVED_LOG;

Back up one copy of each log sequence number by using an operating system utility. This example backs up all logs in the primary archiving location to a disk devoted to log backups:

About the Suspend/Resume Feature

Some third-party tools allow you to mirror a set of disks or logical devices, that is, maintain an exact duplicate of the primary data in another location, and then split the mirror. Splitting the mirror involves separating the copies so that you can use them independently.

With the SUSPEND/RESUME functionality, you can suspend I/O to the database, then split the mirror and make a backup of the split mirror. By using this feature, which complements the backup mode functionality, you can suspend database I/Os so that no new I/O can be performed. You can then access the suspended database to make backups without I/O interference.

You do not need to use SUSPEND/RESUME to make split mirror backups in most cases, although it is necessary if your system requires the database cache to be free of dirty buffers before a volume can be split. Some RAID devices benefit from suspending writes while the split operation is occurring; your RAID vendor can advise you on whether your system would benefit from this feature.

The ALTERSYSTEMSUSPEND statement suspends the database by halting I/Os to datafile headers, datafiles, and control files. When the database is suspended, all pre-existing I/O operations can complete; however, any new database I/O access attempts are queued.

The ALTERSYSTEMSUSPEND and ALTERSYSTEMRESUME statements operate on the database and not just the instance. If the ALTERSYSTEMSUSPEND statement is entered on one system in a RAC configuration, then the internal locking mechanisms propagate the halt request across instances, thereby suspending I/O operations for all active instances in a given cluster.

Making Backups in a Suspended Database

After a successful database suspension, you can back up the database to disk or break the mirrors. Because suspending a database does not guarantee immediate termination of I/O, Oracle Corporation recommends that you precede the ALTERSYSTEMSUSPEND statement with a BEGINBACKUP statement so that the tablespaces are placed in backup mode.

You must use conventional user-managed backup methods to back up split mirrors. RMAN cannot make database backups or copies because these operations require reading the datafile headers. After the database backup is finished or the mirrors are re-silvered, then you can resume normal database operations using the ALTERSYSTEMRESUME statement.

Backing up a suspended database without splitting mirrors can cause an extended database outage because the database is inaccessible during this time. If backups are taken by splitting mirrors, however, then the outage is nominal. The outage time depends on the size of cache to flush, the number of datafiles, and the time required to break the mirror.

Note the following restrictions for the SUSPEND/RESUME feature:

In a RAC configuration, you should not start a new instance while the original nodes are suspended.

No checkpoint is initiated by the ALTERSYSTEMSUSPEND or ALTERSYSTEMRESUME statements.

You cannot issue SHUTDOWN with IMMEDIATE, NORMAL, or TRANSACTIONAL options while the database is suspended.

Issuing SHUTDOWNABORT on a database that was already suspended reactivates the database. This prevents media recovery or crash recovery from hanging.

To make a split mirror backup in SUSPEND mode:

Place the database tablespaces in backup mode. For example, to place tablespace users in backup mode enter:

ALTER TABLESPACE users BEGIN BACKUP;

If you are backing up all of the tablespaces for your database, you can instead use:

ALTER DATABASE BEGIN BACKUP;

If your mirror system has problems with splitting a mirror while disk writes are occurring, then suspend the database. For example, issue the following:

ALTER SYSTEM SUSPEND;

Check to make sure that the database is suspended by querying V$INSTANCE. For example:

A raw device is a disk or partition that does not have a file system. In other words, a raw device can contain only a single file. Backing up files on raw devices poses operating system specific issues. The following sections discuss some of these issues on two of the most common operating systems supporting Oracle: UNIX and Windows.

Backing Up to Raw Devices on UNIX

When backing up to or from raw devices, the UNIX dd command is the most common backup utility. See your operating system specific documentation for complete details about this utility.

The most important aspect of using dd is determining which options to specify. You need to know the following information.

Data

Explanation

Block size

You can specify the size of the buffer that dd uses to copy data. For example, you can specify that dd should copy data in units of 8 KB or 64 KB. Note that the block size for dd need not correspond to either the Oracle block size or the operating system block size: it is merely the size of the buffer used by dd when making the copy.

Raw offset

On some systems, the beginning of the file on the raw device is reserved for use by the operating system. This storage space is called the raw offset. Oracle should not back up or restore these bytes.

Size of Oracle block 0

At the beginning of every Oracle file, the operating system-specific code places an Oracle block called block 0. The generic Oracle code does not recognize this block, but the block is included in the size of the file on the operating system. Typically, this block is the same size as the other Oracle blocks in the file.

The information in the preceding table enables you to set the dd options specified in Table 16-1.

Table 16-1 Options for dd Command

This option ...

Specifies ...

if

The name of the input file, that is, the file that you are reading.

of

The name of the output file, that is, the file to which you are writing.

bs

The buffer size used by dd to copy data.

skip

The number of dd buffers to skip on the input raw device if a raw offset exists. For example, if you are backing up a file on a raw device with a 64 KB raw offset, and the dd buffer size is 8 KB, then you can specify skip=8 so that the copy starts at offset 64 KB.

seek

The number of dd buffers to skip on the output raw device if a raw offset exists. For example, if you are backing up a file onto a raw device with a 64 KB raw offset, and the dd buffer size is 8 KB, then you can specify skip=8 so that the copy starts at offset 64 KB.

count

The number of blocks on the input raw device for dd to copy. It is best to specify the exact number of blocks to copy when copying from raw device to file system, otherwise any extra space at the end of the raw volume that is not used by the Oracle datafile is copied to the file system.

Remember to include block 0 in the total size of the input file. For example, if the dd block size is 8 KB, and you are backing up a 30720 KB datafile, then you can set count=3841. This value for count actually backs up 30728 KB: the extra 8 KB are for Oracle block 0.

Because a raw device can be the input or output device for a backup, you have four possible scenarios for the backup. The possible options for dd depend on which scenario you choose, as illustrated in Table 16-2.

Table 16-2 Scenarios Involving dd Backups

Backing Up from ...

Backing Up to ...

Options Specified for dd Command

Raw device

Raw device

if,of,bs,skip, seek, count

Raw device

File system

if,of,bs,skip, count

File system

Raw device

if,of,bs,seek

File system

File system

if,of,bs

Backing Up with the dd utility on UNIX: Examples

For these examples of dd utility usage, assume the following:

You are backing up a 30720 KB datafile.

The beginning of the datafile has a block 0 of 8 KB.

The raw offset is 64 KB.

You set the dd block size to 8 KB when a raw device is involved in the copy.

In the following example, you back up from one raw device to another raw device:

% dd if=/dev/rsd1b of=/dev/rsd2b bs=8k skip=8 seek=8 count=3841

In the following example, you back up from a raw device to a file system:

% dd if=/dev/rsd1b of=/backup/df1.dbf bs=8k skip=8 count=3841

In the following example, you back up from a file system to a raw device:

% dd if=/backup/df1.dbf of=/dev/rsd2b bs=8k seek=8

In the following example, you back up from a file system to a file system, and so can set the block size to a high value to boost I/O performance:

% dd if=/oracle/dbs/df1.dbf of=/backup/df1.dbf bs=1024k

Backing Up to Raw Devices on Windows

Like UNIX, Windows supports raw disk partitions in which the database can store datafiles, online logs, and control files. Each raw partition is assigned either a drive letter or physical drive number and does not contain a file system. As in UNIX, each raw partition on NT is mapped to a single file.

NT differs from UNIX in the naming convention for Oracle files. On NT, raw datafile names are formatted as follows:

\\.\drive_letter:
\\.\PHYSICALDRIVEdrive_number

For example, the following are possible raw filenames:

\\.\G:
\\.\PHYSICALDRIVE3

Note that you can also create aliases to raw filenames. The standard Oracle database installation provides a SETLINKS utility that can create aliases such as \\.\Datafile12 that point to filenames such as \\.\PHYSICALDRIVE3.

The procedure for making user-managed backups of raw datafiles is basically the same as for copying files on an NT file system, except that you should use the Oracle OCOPY utility rather than the NT-supplied copy.exe or ntbackup.exe utilities. OCOPY supports 64-bit file I/O, physical raw drives, and raw files. Note that OCOPY cannot back up directly to tape.

Testing the Restore of Backups

The best way to test the usability of backups is to restore them to a separate host and attempt to open the database, performing media recovery if necessary. This option requires that you have a separate host available for the restore procedure.

Running the DBVERIFY Utility

The DBVERIFY program is an external command-line utility that performs a physical data structure integrity check on an offline datafile. Use DBVERIFY primarily when you need to ensure that a user-managed backup of a datafile is valid before it is restored or as a diagnostic aid when you have encountered data corruption problems.

The name and location of DBVERIFY is dependent on your operating system. For example, to perform an integrity check on datafile tbs_52.f on UNIX, you can run the dbv command as follows:

Oracle import and export utilities move Oracle data in and out of Oracle databases. Export utilities write exported database objects to operating system files in an Oracle-proprietary format. Import utilities can read the files produced by export utilities and re-create database objects. Logical exports of data can be a useful supplement to physical database backups in some situations, especially in backing up recovery catalog databases.

There are two sets of Oracle database import and export utilities: Original Import and Export (which were used in previous releases) and Data Pump Import and Export (new for Oracle Database Release 10g). The Data Pump utilities offer better performance and more complete support of features of Oracle Database Release 10g. Whichever export tool you use to export objects to a file, you must use the corresponding import tool to import the objects from the file, that is, you cannot use the Data Pump Import utility to read the output of the Original Export utility, or the Original Import to read the output of the Data Pump Export utility.

See Also:

Oracle Database Utilities for complete documentation of the Oracle import and export utilities, including a comparison of their capabilities.

Always back up initialization parameter files, networking and configuration files, and password files. If a media failure destroys these files, then you may have difficulty re-creating your environment. For example, if you back up the database and server parameter file but do not back up the networking files, then you can restore and recover the database but will not be able to authenticate users through Oracle Net until you re-create the networking files.

As a rule, you should back up miscellaneous Oracle files after changing them. For example, if you add or change the net service names that can be used to access the database, then create a new backup of the tnsnames.ora file.

The easiest way to find configuration files is to start in the Oracle home directory and do a recursive search for all files ending in the .ora extension. For example, on UNIX you can run this command:

% find $ORACLE_HOME -name "*.ora" -print

You must use third-party utilities to back up the configuration files. For example, you can use the UNIX cp command to back up the tnsnames.ora and listener.ora files as follows:

You can also use an operating system utility to back up the server parameter file. Although the database does not depend on the existence of a particular version of the server parameter file to be started, you should keep relatively current backups of this file so that you do not lose changes made to the file. Note that if you lose the server parameter file, you can always create a new one or start the instance with a client-side initialization parameter file (PFILE).

One of the most important aspects of user-managed backup and recovery is keeping records of all current database files as well as the backups of these files. For example, you should have records for the location of the following files:

Datafiles and control files

Online and archived redo logs (note that online logs are never backed up)

Initialization parameter files

Password files

Networking-related files

Recording the Locations of Datafiles, Control Files, and Online Redo Logs

The following useful SQL script displays the location of all control files, datafiles, and online redo log files for the database:

SELECT NAME FROM V$DATAFILE
UNION ALL
SELECT MEMBER FROM V$LOGFILE
UNION ALL
SELECT NAME FROM V$CONTROLFILE;

Recording the Locations of Archived Redo Logs

You can determine the location of the default archived log destinations by executing the following SQL script:

SELECT NAME, VALUE
FROM V$PARAMETER
WHERE NAME LIKE log_archive_dest%
AND VALUE IS NOT NULL
/
NAME VALUE
---------------------------------- -------------------------------------------
log_archive_dest_1 LOCATION=/oracle/work/arc_dest/arc
log_archive_dest_state_1 enable

Determine the format for archived logs by running SHOW as follows:

SHOW PARAMETER LOG_ARCHIVE_FORMAT

To see a list of all the archived logs recorded in the control file, issue this query:

SELECT NAME FROM V$ARCHIVED_LOG;

Recording the Locations and Dates of Backup Files

It is not enough to merely record the location of backup files: you must correlate the backups with the original files. If possible, name the backups with the same relative filename as the primary file. Whatever naming system you use, keep a table containing the relevant information. For example, you could keep the following table as a record of database file locations in case of a restore emergency.